Thread Mic and Internal Threading

[mikey]

Before i threaded the external 15/16 - 16 i turned it down to .934" a couple thousands below the nominal .9375" will that create slop in the threads?

Should be okay. You are in the OD range for either a class 2 or 3 fit. It is good to know that the "fit" depends on both the OD and the pitch diameter being in your desired range. You can have a class 3a OD but if the pitch diameter you hit falls into the class 2a range, there may be some slop so I suggest you work carefully with the internal threading.

 

[gun410]

Should be okay. You are in the OD range for either a class 2 or 3 fit. It is good to know that the "fit" depends on both the OD and the pitch diameter being in your desired range. You can have a class 3a OD but if the pitch diameter you hit falls into the class 2a range, there may be some slop so I suggest you work carefully with the internal threading.

Ok, I'm starting to catch on, the pitch diameter was .897 so on the high side of a class 3 fit, I'm just curious if having a pitch on the high side and the diameter on the lower side will negatively effect, but the pitch and od are still close to a class 3 fit. Since i still don't have the micro 100 threading bar I decided to work on the baffles. After putting a 2" long 1.5"D 17-4 blank in the 3 jaw, i center drilled, drilled the bore 1/4" and was going to drill 11/32" before reaming .375" but for some reason when i took the 1/4" bit out and tried drilling with the 11/32 bit it just wouldn't drill and was chattering quite a bit. I thought it was the drill bit but it seems sharp. My lathe is sittting on a tool cabinet that moves around a little so i know it's not leveled, I'm hoping that isn't causing the problem, because I would need to Re-make the break if the concentricy was off when drilling on my lathe.

 

[mikey]

I'm not sure what is going on with your drill but if I had to guess, it is not sharpened well. The geometry may be off even if it is sharp. Are you using high quality drill bits?

I won't go into how to choose a reamer for a precision ID but I will tell you how I use one. I use a spotting drill, not a center drill. For my pre-reamer drill I choose the size carefully but it usually winds up pretty close to 0.003 - 0.005" under the reamer size. I spot the hole, drill with a drill that is one size smaller than the pre-reamer drill, then I use the pre-reamer drill. Then I use the reamer. The reason for this sequence is to debulk the hole with maximum accuracy and then skim cut it pretty straight with the pre-reamer drill; this then allows the reamer a decent chance of cutting evenly. Ideally, and especially on a critical work piece that must be concentric and true, I will pre-drill small, then bore the hole to the pre-reamer size before reaming. Drills make holes but they are not round and they are not straight. A reamer will follow that not straight hole and it will cut a bent hole that is on size. Remember that if the reamed hole must be dead straight, you must bore it straight; you cannot drill it straight.

Insofar as concentricity is concerned, as long as you do not remove the work piece from the 3 jaw you should be fine. Remove it and it will take a 4 jaw to get it realigned.

 

[gun410]

I'm not sure what is going on with your drill but if I had to guess, it is not sharpened well. The geometry may be off even if it is sharp. Are you using high quality drill bits?

I won't go into how to choose a reamer for a precision ID but I will tell you how I use one. I use a spotting drill, not a center drill. For my pre-reamer drill I choose the size carefully but it usually winds up pretty close to 0.003 - 0.005" under the reamer size. I spot the hole, drill with a drill that is one size smaller than the pre-reamer drill, then I use the pre-reamer drill. Then I use the reamer. The reason for this sequence is to debulk the hole with maximum accuracy and then skim cut it pretty straight with the pre-reamer drill; this then allows the reamer a decent chance of cutting evenly. Ideally, and especially on a critical work piece that must be concentric and true, I will pre-drill small, then bore the hole to the pre-reamer size before reaming. Drills make holes but they are not round and they are not straight. A reamer will follow that not straight hole and it will cut a bent hole that is on size. Remember that if the reamed hole must be dead straight, you must bore it straight; you cannot drill it straight.

Insofar as concentricity is concerned, as long as you do not remove the work piece from the 3 jaw you should be fine. Remove it and it will take a 4 jaw to get it realigned.

I guess it was the drill bit, I bought a 23/64 (.359”) drill bit and it cut just fine. I heard that your supposed to leave 1/64 for reaming, but i guess .016” is to much to ream. I don’t think I have a boring bar small enough to fit into bore. Is a spotting drill more accurate than a center drill? The muzzle breaks were held in a 3 jaw and turned and threaded in 1 setup.

 

[mikey]

If you do it the right way, choosing a pre-reamer drill is almost as complicated as choosing a reamer to come in on a specific size because the material you are working with influences your choices. I'm attaching a doc that explains this statement.

I suspect most hobby guys buy a set of on-size reamers and expect to have holes of those sizes after reaming. The typical advice is to just pick a drill about 0.005" smaller than the reamer. This usually results in a hole that is off-size a few thou, depending on the pre-reamer drill, the reamer and the material. This is usually not a problem because we can make whatever fits in the hole to suit but if the hole must be a certain size then you have to go through a number of steps to choose the right drill and reamer and you have to know how to ream. This gets really expensive when you have to order a specific reamer for a critical hole.

Instead of buying specialty reamers, the best option for a hobby guy is to just bore the hole. Way cheaper and potentially more accurate because if you're really good at boring you can come in on size within the low tenths and you can often match or even beat the finish. I own multiple sets of reamers but I don't use them as often nowadays. It is so much faster and more accurate for me to just bore the stupid hole so I can get on with it. Nowadays, I mostly use a reamer in shallower through holes that I have to fit a pin into, and I can cut the pin to fit the hole I make. Otherwise, I bore it.

You are working with components that require good fits. If you plan to do a lot of this kind of work then it is going to be worth it to learn to bore a hole. This will mean spending money on good bars to fit the holes you require. It also requires that you spend the time to learn to bore accurately, which is not a bad skill to have if you ask me.

A spotting drill is not more accurate than a center drill but it does allow a drill to start more accurately so when you must optimize concentricity and accuracy, a spotter is preferred. I almost never use a center drill except on the end of a work piece to accept a live center. With that said, machinists have been using center drills for decades to start holes with and probably the majority feel this is the preferred tool. We had a good discussion on spotters here. I guess I should also emphasize that when using any drill, and especially when you're trying to maximize accuracy, start with a spotter and then peck and go slowly with your drill until the tips of the flutes are buried in the hole; then you can increase feed and pressure. Try it and you'll see that it is the most effective way to start a drill in a hole.

EDIT: almost forgot to add that you should make sure you put a 45 degree chamfer at the entrance to the hole before using a reamer. This will greatly reduce the chatter than can occur at the start.

 

[gun410]

If you do it the right way, choosing a pre-reamer drill is almost as complicated as choosing a reamer to come in on a specific size because the material you are working with influences your choices. I'm attaching a doc that explains this statement.

I suspect most hobby guys buy a set of on-size reamers and expect to have holes of those sizes after reaming. The typical advice is to just pick a drill about 0.005" smaller than the reamer. This usually results in a hole that is off-size a few thou, depending on the pre-reamer drill, the reamer and the material. This is usually not a problem because we can make whatever fits in the hole to suit but if the hole must be a certain size then you have to go through a number of steps to choose the right drill and reamer and you have to know how to ream. This gets really expensive when you have to order a specific reamer for a critical hole.

Instead of buying specialty reamers, the best option for a hobby guy is to just bore the hole. Way cheaper and potentially more accurate because if you're really good at boring you can come in on size within the low tenths and you can often match or even beat the finish. I own multiple sets of reamers but I don't use them as often nowadays. It is so much faster and more accurate for me to just bore the stupid hole so I can get on with it. Nowadays, I mostly use a reamer in shallower through holes that I have to fit a pin into, and I can cut the pin to fit the hole I make. Otherwise, I bore it.

You are working with components that require good fits. If you plan to do a lot of this kind of work then it is going to be worth it to learn to bore a hole. This will mean spending money on good bars to fit the holes you require. It also requires that you spend the time to learn to bore accurately, which is not a bad skill to have if you ask me.

A spotting drill is not more accurate than a center drill but it does allow a drill to start more accurately so when you must optimize concentricity and accuracy, a spotter is preferred. I almost never use a center drill except on the end of a work piece to accept a live center. With that said, machinists have been using center drills for decades to start holes with and probably the majority feel this is the preferred tool. We had a good discussion on spotters here. I guess I should also emphasize that when using any drill, and especially when you're trying to maximize accuracy, start with a spotter and then peck and go slowly with your drill until the tips of the flutes are buried in the hole; then you can increase feed and pressure. Try it and you'll see that it is the most effective way to start a drill in a hole.

EDIT: almost forgot to add that you should make sure you put a 45 degree chamfer at the entrance to the hole before using a reamer. This will greatly reduce the chatter than can occur at the start.

The best option diffidently sounds like boring vs buying a bunch of custom drill bits. I have bored before using a micro 100 bar but it broke and now all i have are Chinese carbide insert boring bars. I actually do have a small boring bar to fit the hole (4mm) but the when the insert is at a significant angle is that from it being a cheap chinese tool or is that how its supposed to be? Also with this small of a boring bar its too small to be able to use in my tool post holders, I guess i will have to make some sort of adapter. Also the micro 100 threading bar came in but I'll need to be able to bore before threading. When boring does it matter accuracy wise if you use the carriage feed vs turning the dial?

One of the youtubers i watch just came out with a review on these small carbide boring bars that seem to work good for pretty cheap. I'm thinking about picking some up, anyone else use these before? https://www.banggood.com/Drillpro-2...2931.html?rmmds=buy&ID=41227&cur_warehouse=CN

I appreciate the guide you've gave, will help a ton when drilling

 

[mikey]

To save me time and typing, please review this thing.

The boring bar in pic#1 is a negative rake bar. The flat on top orients the bar. This is going to produce a nice finish but the cutting forces will be very high; personally, I avoid this type of bar.

You should invest in an Aloris AXA-4D and then make some adapters to hold smaller bars. See the article above for ideas. Alternatively, you can make something like this to fit your current holder and your smaller bars.

 

[gun410]

To save me time and typing, please review this thing.

The boring bar in pic#1 is a negative rake bar. The flat on top orients the bar. This is going to produce a nice finish but the cutting forces will be very high; personally, I avoid this type of bar.

You should invest in an Aloris AXA-4D and then make some adapters to hold smaller bars. See the article above for ideas. Alternatively, you can make something like this to fit your current holder and your smaller bars.

Thank you for that link, I’ve looked for something like boring for beginners but have never found something that detailed.

I don’t have an Aloris AXA-4d but my import QCTP came with a boring bar holder for 5/8 and 3/4. Are you suggesting the buying an new Aloris QCTP or just the boring bar holder because of its even clamping design, would it fit on my import QCTP?

I actually do have a telescoping gauge set, I thought it was lost. I measured the 23/64 hole I previously drilled and it was .368” not sure why it came out oversized, but since that’s .007” away from my reamer size I decided to ream it.
The reamed hole came out .385”, .01 bigger than my reamer, not sure how that happened. That little extra room the reamer made won’t effect the suppressor’s performance but I would like to figure this problem out. I also should mention that my lathe isn’t leveled due to it being on a rolling tool cabinet.

 

[mikey]

Thank you for that link, I’ve looked for something like boring for beginners but have never found something that detailed.

I don’t have an Aloris AXA-4d but my import QCTP came with a boring bar holder for 5/8 and 3/4. Are you suggesting the buying an new Aloris QCTP or just the boring bar holder because of its even clamping design, would it fit on my import QCTP?

You're welcome. Hope it helps you to bore better.

I am not suggesting that you buy an Aloris tool post! I do, however, suggest you buy an Aloris AXA 4D if you plan to do a lot of boring. And yes, it will fit your import AXA tool post. The boring bar holder you show in your pics is the typical import type that pushes against the bar at just two points with cotters; those cotters contact a steel sleeve inside the bore of the holder. This is not a secure way to hold a boring bar and will contribute to chatter in the bore. In contrast, the Aloris 4D squeezes down on the entire bar so that it cannot move once it is locked down. The only way to get it more solid is to use a heat shrink bar holder. As I said in the article, the holder is more important than the bar and it is worth buying or making a really good one.

The 4D also allows you to make sleeves to fit your smaller bars into it, making it possible to use every boring bar you have in one holder. Not sure that its practical to do that for your really small bars and it might be better to make a tool holder out of aluminum with a smaller bore in the holder to fit smaller bars. I suggest a 3/8" bore if you do this.

I actually do have a telescoping gauge set, I thought it was lost. I measured the 23/64 hole I previously drilled and it was .368” not sure why it came out oversized, but since that’s .007” away from my reamer size I decided to ream it.
The reamed hole came out .385”, .01 bigger than my reamer, not sure how that happened. That little extra room the reamer made won’t effect the suppressor’s performance but I would like to figure this problem out. I also should mention that my lathe isn’t leveled due to it being on a rolling tool cabinet.

There are a number of reasons why a drill will drill oversize. The main one is because the geometry is off. If you take a drill gauge to your drills you will find that many drills are not ground dead on symmetrical, especially imported sets. What brand of drills are you using and are they jobber drills? Other reasons include drills that are not sharp, have improper relief angles, excessive web thickness (required more feed pressure to cut, which can exacerbate any asymmetry in the geometry) and then there is the human factor.

One of the key human factors is improper feed. I know drilling a hole may not seem like a big deal but for all cutting tools, performance is enhanced when the tool cuts continuously but without being forced into the cut. This is a feel thing. You must feed so there is a slight positive resistance to the feed so the tool cuts as efficiently as it can. This also allows the chip clearance features of the tool to work as they should. I have seen so many guys crank on the feed pressure as much as they can, thinking that is the right way to go. The drill comes out of the hole smoking hot and they wonder why their drills don't last long. My drills are almost cool to the touch after drilling but they cut fast and they stay sharp. The trick is to slow down the speed a little bit and feed properly. This allows the drill to cut accurately and your hole sizes will be closer to what they should be.

I'm not surprised your reamer produced an oversized hole but as to why, I can only guess. I suspect that your pre-reamer hole was not straight and not consistently sized for the reasons discussed above. The reamer will try to follow that hole and if it cannot follow precisely then it will cut oversized as it cuts off the bends in the hole.

Another reason for reaming oversize is improper speeds and technique. You will find that for reamers above about 3/8", it is best to slow down. I run my reamers at about 100 rpm and again, feed so that there is a slight positive resistance to feed. I do not bottom out the reamer and I stop the machine when I finish the infeed before withdrawing the reamer; I do not retract the reamer with the machine running. I have reamers that are nearly 30 years old and are still sharp and accurate so this works for me.

The level of the lathe can have an impact on boring but it will be minimal. Most of your results are so oversized that I suspect the quality of your tools and the way you're using them is having more of an impact. The good thing is that this is easy to fix ... buy good tools and learn to use them well. Please know that I'm not criticizing you or dissing your stuff. I'm simply pointing out that you are trying to do precision work and that requires a realistic approach.

Okay, tired of typing.

 

[benmychree]

It is not at all necessary to use inserts to thread, internal or external, nor is micrograin carbide necessary for most materials to be cut; for nearly all work, HSS is all that one needs, for external, Aloris makes a tool that only needs to be sharpened on top and has a very long service life, and Bokum makes internal threading bars that are form relieved and are also only sharpened on top, also long lived, These tools are much more durable and forgiving in terms of not being easily broken/damaged as carbide tools are.